背景

有时候我们需要维护一个，有顺序的数组，如数据源带有优先级的，低优先级排起数组前面，高优先级排素组后面。为了动态高效维护该“数组”，可以用CFBinaryHeapCreate。

CFBinaryHeapCreate

Creates a new mutable or fixed-mutable binary heap.

简要代码演示：

- (instancetype)init
{
    if (self = [super init]) {
        CFBinaryHeapCallBacks callbacks = (CFBinaryHeapCallBacks) {
            .version = 0,
            .retain = &KGModuleItemPriorityRetain,
            .release = &KGModuleItemPriorityRelease,
            .copyDescription = &CFCopyDescription,
            .compare = &KGModuleItemPriorityCompare
        };
        
        _modules = CFBinaryHeapCreate(kCFAllocatorDefault, 0, &callbacks, NULL);
        _moduleCache = [NSMutableDictionary dictionary];
    }
    
    return self;
}

static const void *KGModuleItemPriorityRetain(CFAllocatorRef allocator, const void *ptr) {
    return CFRetain(ptr);
}

static void KGModuleItemPriorityRelease(CFAllocatorRef allocator, const void *ptr) {
    CFRelease(ptr);
}

static CFComparisonResult KGModuleItemPriorityCompare(const void *ptr1, const void *ptr2, void *info)
{
    KGAppModuleModel *item1 = (__bridge KGAppModuleModel *)ptr1;
    KGAppModuleModel *item2 = (__bridge KGAppModuleModel *)ptr2;
    
    if (item1.priority < item2.priority) {  // greator first
        return kCFCompareLessThan;
    }
    
    if (item1.priority > item2.priority) {
        return kCFCompareGreaterThan;
    }
    
    if (item1.sequence > item2.sequence) {  // lesser first
        return kCFCompareLessThan;
    }
    
    if (item1.sequence < item2.sequence) {
        return kCFCompareGreaterThan;
    }
    
    return kCFCompareEqualTo;
}

- (void)kgEnumerateModulesUsingBlock:(__attribute__((noescape)) void (^)(id module, BOOL *stop))block
{
    CFIndex count = CFBinaryHeapGetCount(_modules);
    const void **list = calloc(count, sizeof(const void *));
    CFBinaryHeapGetValues(_modules, list);
    
    CFArrayRef objects = CFArrayCreate(kCFAllocatorDefault, list, count, &kCFTypeArrayCallBacks);
    
    NSArray *items = (__bridge_transfer NSArray *)objects;
    
    [items enumerateObjectsWithOptions:NSEnumerationReverse
                            usingBlock:^(KGAppModuleModel * _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
                                block(obj.module, stop);
                            }];
}

备注：

CFBinaryHeapAddValue，该函数作用，把对象加入CF管理，同时把OC管理的对象生命周期CF管理，会触发KGModuleItemPriorityRetain。

CFBinaryHeapGetValues，该函数作用是把之前加入对堆的数据取出来，存入到一个我们自定义的C数组里面去，取出来的结果是根据我们的排序规则KGModuleItemPriorityCompare排序的，是有序的。该函数会触发KGModuleItemPriorityRetain，本质是调用了CFBinaryHeapAddValue，也会触发KGModuleItemPriorityRelease。